What to do Now?

[HuricaneKatt]

Sorry, I do not know the water condition. Also, I have NO clue what the species was, I am not even sure it was a "purple sea urchin" (I never mentioned that so I'm not sure where you got it lol). I'd have to ask my roommate as she ordered him specially for me when I told her I really really wanted a sea urchin. I do know that he lived a year in the tank and was very healthy, active and vibrant. He was starting to lose spikes, but he had done that once before and recovered. But then he got this white stuff on his spikes and died before we could do anything or research more on what to do. My roommate just did a water change before he died, so that may have stressed him out and sped up his death. I know that we got a new light, a stronger one, and started getting really bad red algae and it was round that time that he started losing spikes. Could the light and or the algae have had something to do with his death?
I don't know where, but right after she noticed him dead my roommate did a search and found a few places that said they release really bad toxins when they die, and even one personal story about a person who lost his whole tank (like us) after his urchin died. Within a few hours (not sure how long he was dead, but he was alive in the am and dead when we got home at night) the clown fishes' gills were puffy and frayed and they both died. One early in the night, one a bit later. The blue/black fish (he looks like this pic below: some type of damsel) was not looking too great at first, but he seems to be ok now...

 

[HuricaneKatt]

Here is Spike in all of his Glory...
RIP

The pink, blue, and the blue/yellow fish we no longer have. I don't rembmer what happened with them, old pics. lol I can't find any pics of the yellow fish...

 

[Cerianthus]

Did I mistaken for other thread on Purple urchin?? Possibly!

This is common Long spine Urchin, Diadema Sp, which I doubt caused release of enough toxins to crash the whole tank.
If you kept it for year, you done very well, IMO. Lot longer than some of mine and some people I know. Massive fluctuation in salinity or simple massive water changes can cause their death.
Maybe tank ran out of algae/macros which they most survived on and/or lack of other necessary dissoved solids, calcium, etc. etc..

It could also been your water condition. I would always have test kits until you can visibly identified fouling of water (takes some time and many tanks).

Like I said, youve done well if you had it for a year.

Good Luck with new venture.

BTW, damsel in pic is pretty nasty damsel.

 

[HuricaneKatt]

That's just a pic from Google search, but it looks exactly like ours, so thanks lol I think we are going to do 1 seahorse/invert tank and one fish tank...